Field of the invention
The present invention relates to a secondary battery, and more particularly to a pouch type lithium secondary battery which has an electrode assembly received in a pouch.
Description of the Prior Art
Secondary batteries use a non-aqueous electrolyte because of the reactivity between lithium and water. The non-aqueous electrolyte may be a solid polymer containing lithium salts, or liquid in which lithium salts are dissociated from organic solvent.
The secondary batteries can be classified, according to the kind of electrolyte, into a lithium metal battery and a lithium ion battery which use a liquid electrolyte, and a lithium ion polymer battery using polymer solid electrolyte.
In complete solid type lithium ion polymer batteries, there is no problem of leakage of the organic electrolyte. In gel type lithium ion polymer batteries containing organic electrolyte, the leakage of the electrolyte also can be easily prevented in comparison with lithium ion batteries using liquid electrolyte. For example, the lithium ion polymer battery may use a pouch as a case for an electrode assembly, instead of a metal can.
The pouch is made of multi-layer film generally having a metal foil layer and a synthetic resin layer covering the metal foil layer. The pouch makes it possible to remarkably reduce the weight of the battery, in comparison to when the metal can is used as the case for the electrode assembly. In the multilayer pouch, the foil is generally made of an aluminum material. The polymer layer forming an inner layer of the pouch protects the metal foil from the electrolyte, and prevents an electric short-circuiting between anode and cathode, and electrode tabs.
In order to form a pouch type lithium secondary battery, first, an anode plate, a separator, and a cathode plate are sequentially stacked and then rolled so as to form is an electrode assembly. Next, the electrode assembly is disposed in a fitted pouch. Then, upper and lower pouch films are heated and fusion-welded at open edge of the pouch so as to seal the pouch, thereby forming the pouch type bare cell battery.
Such a bare cell battery may form an inner pack type battery. The inner pack type battery refers to a battery like a bare cell battery which is directly inserted into the body of an electronic device such as a digital camera or a digital camcorder requiring the secondary battery and which is then covered with a cover member forming an exterior surface of the electronic device. The inner pack type battery has an excellent merit of enduring exterior impact.
Specifically, elements or structure, such as a protection circuit module connected to the electrodes of the bare cell battery, or a positive temperature coefficient element, is mounted in the body of the electronic device.
Therefore, in the case of the inner pack type secondary battery in which a protection circuit module, a positive temperature coefficient element, etc. are mounted in a body of an electronic device, just the protection circuit module can be replaced with a new module when a protection circuit is damaged. Therefore, the inner pack type secondary battery has an improved yield and a less chance of being exposed to exterior impact, in comparison with the secondary battery integrated with the protection circuit module.
However, the conventional secondary battery where the electrode assembly is received in the soft pouch has a problem in that a soft pouch may be easily damaged during mounting of the secondary battery in the electronic device.